1. Field of the Invention
The present invention relates to a belt device for use in an image forming apparatus.
2. Description of the Related Art
Conventionally, in the image forming apparatus such as the copying machine and the printer, a tandem color image forming apparatus including the intermediate transfer belt (belt device) has been known (for example, see Japanese Patent Application Laid-open No. 2006-343629, Japanese Patent Application Laid-open No. 2001-83840, and Japanese Patent No. 3755356).
More specifically, four photosensitive drums (image carriers) are arranged in proximity in a row arrangement, facing the intermediate transfer belt (belt device). With these four photosensitive drums, black, yellow, magenta, and cyan toner images are respectively formed. Respective color toner images formed by the respective photosensitive drums are superposed and transferred on the intermediate transfer belt. A plurality of color toner images carried on the intermediate transfer belt are transferred onto a recording medium as a color image.
In the above type of image forming apparatus, such a technique has been known that a widthwise displacement of the intermediate transfer belt is detected to correct the widthwise displacement of the intermediate transfer belt based on the detection result (for example, see Japanese Patent Application Laid-open No. 2006-343629, Japanese Patent Application Laid-open No. 2001-83840, and Japanese Patent No. 3755356). It is an object of such a technique to suppress problems that the quality of the color image degrades due to meandering of the intermediate transfer belt and that after the intermediate transfer belt is displaced largely in a width direction (misalignment of the belt), the intermediate transfer belt comes in contact with another member to damage the intermediate transfer belt.
Specifically, in Japanese Patent Application Laid-open No. 2006-343629, a first detector (displacement sensor) detects a displacement magnitude of a contact that abuts against an end in the width direction of the intermediate transfer belt (endless belt) and swings by following the displacement. A correcting unit (meandering correcting roller) corrects the displacement (meandering) of the intermediate transfer belt based on the detection result of the first detector. When the intermediate transfer belt meanders exceeding a detection range (boundary of malfunction detection) of the first detector, it is determined that the apparatus has malfunction and drive of the intermediate transfer belt is stopped.
Further, in Japanese Patent Application Laid-open No. 2006-343629, a second detector (edge sensor) is arranged at a position away from the first detector (displacement sensor) widthwise outward. When the second detector detects an edge of the intermediate transfer belt, it is also determined that the intermediate transfer belt meanders further largely due to malfunction of the apparatus, and the drive of the intermediate transfer belt is stopped.
Meanwhile, Japanese Patent No. 3755356 discloses a technique of an image forming apparatus that corrects the displacement (meandering) of the intermediate transfer belt by using a correcting unit (steering roller) based on a detection result of a first detector (edge sensor), where malfunction detection by the first detector (edge sensor) is not performed for a predetermined time from turning the power of the apparatus on. This technique is for preventing a problem that immediately after replacement of the intermediate transfer belt, meandering of the intermediate transfer belt is mistakenly detected as malfunction, although the intermediate transfer belt is normally driven.
In the technique disclosed in Japanese Patent Application Laid-open No. 2006-343629, immediately after replacement of the intermediate transfer belt, meandering of the intermediate transfer belt can be mistakenly detected as malfunction, although the intermediate transfer belt is normally driven.
More specifically, the replaced belt member can be assembled widthwise deviated from a target position, depending on the skill level of the operator. In such a case, if there is originally no malfunction in the belt device, the correcting unit will correct the position of the belt member to the target position at the time of initialization after turning the power on. However, it is determined that the belt member meanders exceeding the detection range of the first detector due to malfunction of the apparatus, and the drive of the intermediate transfer belt is stopped. Accordingly, the image forming apparatus is uselessly shut down, or a useless maintenance operation is performed.
On the other hand, in the technique disclosed in Japanese Patent No. 3755356, because malfunction detection by the first detector is not performed for a predetermined time from turning the power of the apparatus on, there can be expected an effect of suppressing a problem that meandering of the intermediate transfer belt is mistakenly detected immediately after replacement of the intermediate transfer belt, although the intermediate transfer belt is normally driven.
However, in the technique disclosed in Japanese Patent No. 3755356, a second detector that detects large meandering of the belt member is not provided separately from the first detector. Therefore, if the belt device essentially has malfunction, not due to the assembly accuracy of the belt member, the malfunction cannot be detected, and thus, there is a high possibility that a newly replaced belt member can be damaged.
Such a problem cannot be ignored, particularly, in a high-speed machine in which the belt member is driven at a high speed (an image forming apparatus with greater process linear velocity).
This problem is not limited to the belt device using the intermediate transfer belt as the belt member. In other words, this is a common problem in belt devices that detect and correct displacement of the belt member, such as a belt device using the transfer carrier belt as the belt member and a belt device using the photosensitive belt as the belt member.